Technological development and increased demand for mobile equipment have led to a rapid increase in the demand for secondary batteries as an energy source. Among these secondary batteries, a great deal of research and study has been focused on a lithium secondary battery having high energy density and discharge voltage and thus some of such lithium secondary batteries are commercially available and widely used.
The lithium secondary battery comprises a cathode, an anode, a separator and an electrolyte as electric power-generating elements, and generally a variety of additives. Categories of these additives may be broadly divided into those which are essentially required for the operation process of the battery, and those which are additionally required for securing desired performance and/or stability of the battery. Generally, the former essential additives of the battery are added during preparation (fabrication) of the battery components and the latter additional additives are added during preparing processes of the battery components or during assembly processes of the battery.
Of those additives, additives necessary for securing stability of the battery are required at a certain time point, for example, upon occurrence of over current or high temperature due to abnormal operation of the battery, while some additives are continuously needed at a constant level during the use of the battery. For example, electrolyte additives for improvement of a lifespan exert lifespan-extension effects by the use thereof for formation of a firm solid electrolyte interface (SEI) layer on a surface of an electrode during the initial formation process of the battery or for restoration of the SEI layer partially damaged during repeated charge/discharge processes. Therefore, relatively large amounts of additives are consumed during the initial formation process of the battery, whereas only small amounts of additives are required upon subsequent charge/discharge or prolonged storage. If amounts of additives incorporated into the battery are small and consequently total amounts of additives are completely consumed during the initial formation process of the battery, degradation of the battery lifespan occurs upon subsequent charge/discharge or prolonged storage of the battery. However, if amounts of additives are excessively large, reaction of surplus additives results in occurrence of irreversible capacity or decomposition of surplus additives results in deterioration of battery stability due to generation of gas.
Therefore, there is a need for a novel method capable of inhibiting deterioration of battery performance due to the presence of surplus additives, by minimizing adverse side reactions of surplus additives while also exerting inherent effects of additives, via release of only a necessary amount of additives into the electrolyte or electrode.